Scientists say there’s no evidence that popular, well-advertised weight-loss programs can actually help keep the pounds off for long.

According to the new study, conducted by researches at the University of Pennsylvania, evaluating the nation’s 10 favorite diet regimes, data on their long-term success rates are not highly promising.

“We hope that doctors and patients will use this information to make more informed decisions,” said Thomas Wadden, a weight-loss expert at the University of Pennsylvania, in his report that appeared in the Annals of Internal Medicine.

“There are no data on weight loss when you go to a health club, either,” he added, stressing that the lack of scientific proof isn’t an attack on diet programs alone.

The only program that showed strong results in helping people lose weight and maintain it that way was Weight Watchers. Participants of the study lost around 5 per cent of their initial weight in six months and were able to keep about half of it off two years later.

Weight Watchers International operates in the United States, Canada, Mexico, the United Kingdom, Continental Europe, Australia, New Zealand, South Africa and Brazil, offering weight-loss and control programs through the operation of classroom type meetings. The company’s approach towards weight loss and control is based on four core elements: group support, behavior modification, healthful eating and exercise.